|
| Author |
Message |
    
paul_brooking
| | Posted on Sunday, October 06, 2002 - 05:47 am: | 
|
I thought you may be interested in a stuart twin P55 I am working on. There has been
a bit of work recovering it from the state I found it in, the main problem being a
bent crankshaft. I managed to straighten the original crank, re-align the main journals,
and re-grind the flywheel mount for fine re-alignment of the flywheel. Now all seems OK
and I have had it running. Your site was useful for puting me intouch with Fairways, to get some
spares (piston ring and main ball bearing). I am working on some modifications to make it a bit
better than the original design. The idea is to inject fuel through the transfer port into the
cylinder with oil directly pumped to bearings, all under microprocseeor control
(the electronics bit is the easy bit for me). Controling the correct amount of fuel to inject
is actually very easy, because I can make it run on a hit and miss cycle to control the speed
(like a bolinder) so for a given speed the amount of fuel is constant, and there is no need
for a butterfly in the air intake. I've got ordinary car petrol injectors in the transfer ports.
But have not had this running yet. If the fuel is injected after the exhaust port is closed,
the effeciency and environmental performance of a two stroke is better than a conventional
four stroke. I am wondering how close I could get to this ideal with transfer port injection?
There are several reasons It will work better on this engine than a modern engine;
(1) slower speed so better timing accuracy, (2) deflector type piston, (3) with the govenor which
only injects a full charge, it should be possible to tune the dynamics better than with normal
throttle control. Has anyone had experience (or interested) with fuel injection of this type
on modern or old engine? If I should ever get to put it in a boat LPG would be the thing. |
J.B. Castagnos
| | Posted on Sunday, October 06, 2002 - 11:28 am: |
|
I don't think you will be able to control speed on fuel alone, you'll end up with a very lean mixture at idle. Hit and miss may work but it won't be a smooth running engine. You can't inject fuel into the transfer port and have it enter the cylinder before the exhaust port closes, the intake port has to be opened after the exhaust port so it will close before the exhaust port. |
captainbill
| | Posted on Sunday, October 06, 2002 - 11:11 pm: |
|
Paul, Direct Injection lean burn two strokes are here now! My question is, why would you want to use a 50 - 100 year old "platform" to modernise? I agree a Schebler carburetor isn't likely to provide you with a stoichiometric burn but replacing it with injectors and microprocessors? I may be wrong but I'll play the hand the original manufacturer delt me and try to perfect the sience of that period. Bill |
paul_brooking
| | Posted on Monday, October 07, 2002 - 02:33 pm: |
|
J.B.Thanks for the reply, It is great to talk to people about these interesting things.
I should have explained a bit better what I meant, I am focused on what I am doing and
forgett other people won't be thinking along the same lines.
I was refering to other systems called "direct injection" which inject into the cylinder
when the ports are closed, this is the best way. What I am intending to do is inject
with ports open (for reasons of simplicity). I am wondering how well I will be able to
tune the system (injection timing etc) to minimise fuel loss through the exh. port.
The basic idea is to allow the burnt gases to leave, and fill the cylinder with air, before
the fuel is put in at the last moment. I have actually heard of engines at the early 1900s
using this technique.
The system of speed control is to always use a constant quantity of fuel at injection
(which may be adjusted slightly for starting and other requirements) But inhibit
fuel injection on some cycles by a governor to allow speed control .
The engine has such a big fly wheel that I don't think the speed variation
will be too much between pulses.
In other words the mixture will always be adjusted to be optimium, and the engine
will either fire a full charge or no charge, depending on the speed control system.
If the engine is forced to "four-stroke" the power will be halved (for a given speed).
I have not heard of this form of speed control in marine engines, except on the
bolinder (and I don't know if this facility was realy intended for
idle or power control). I would be interested to hear about any other engines of this type
using hit/miss govenors.
********************************************
Captainbill Thanks for the reply.
************************************************
I was hoping nobody would ask that question. I don't know.
I think it is partly that I like playing with old engines. It would be nice to have a boat using
one of these good old engines but without the poor fuel economy and blue haze.
It is not so much a case of using the engine as a platform, as making some small mechanical
changes to the engine, which will be hardly noticable in apearance, to make the engine a bit
more practical. |
captain Bill
| | Posted on Tuesday, October 08, 2002 - 11:21 am: |
|
Poor fuel economy and blue haze associated with early two stroke marine engines in use today has much to do with improper fuel/oil ratios and worn-out systems that fuel injection will not cure. Since intake and exhaust ports are "cast in" your timming will remain the same unless you alter these ports or alter the piston, or a combination of the above. Delayed fuel injection will not reduce fuel loss through the exhaust port at full throttle setting. These engines were designed to power displacement hulls and run at full throttle, speed regulation for docking only! It comes down to fuel atomization which can be done quite effectively with a mixing valve or early carburetor of proper size. Bill |
paul_brooking
| | Posted on Tuesday, October 08, 2002 - 01:51 pm: |
|
I think the advantage of fuel injection is that the fuel may enter the cylinder after the reflected exhaust pulse (due to the exhaust box), rather than enter before it as it did originally. I should think it is when the cylinder pressure is sucked down very low by the fast moving exhaust gases, that some of an incomming charge may be sucked through the exhaust port. With a well set up exhaust system the flow around the exhaust port should be more stable after the reflected pulse.
A good thing about boat engines is that the speed only varies a small amount, SO the exhaust resonance optimum does not change much. Presumably the exhaust box has been made with the correct resonance ?
I do think these old engines are wonderful things, I hope people don't take my tampering with them as a lack of respect for them.
Paul. |
paul_brooking
| | Posted on Wednesday, October 09, 2002 - 04:20 am: |
|
After a scribble on the back of a fag packet I realise that the exhaust system resonance
of this engine is much more connected with the cylinder volume and exhaust port area, than the
exhaust box.
Paul |
|
|
|
|
